I have to say 383 for a couple of reasons, some technical, some personal. first of all, yes, a 400 is bigger than a 383 but which sounds more intimidating. To me, the #s 383 just look more interesting than 400. I also like the low down torque of the 383. now don't get me wrong, I know the outputs can be very similar, but it just seems to me that of all the engines i've seen, the 383 hit their peak torque #s lower in the rpm range.